The precursor to the Internet, created by scientists at the United States Defense Advanced Research Project Agency (DARPA). Also known as the DARPAnet.

•Brute force attack

An attack in which a hacker tries to determine a password or method of entry into a system by continuously bombarding it with requests.

•Buffer overflow

A programming mistake in which the length and content of incoming data is not verified and overwhelms the program. This is the most common avenue for hackers to break into software.

•Cracker

One who breaks into a computer or network system in order to corrupt or steal data. Distinguished from hacker because of a cracker's malevolent intent.

•Denial of service attack (DoS)

Designed to lock legitimate users out of Web sites or networks by overwhelming a system with useless traffic so that the computer is not able to respond to any other requests.

•Distributed denial of service attack (DdoS)

An automated denial of service attack that runs simultaneously from multiple computers.

•DNS

Domain Name System; a system to matches Internet names to IP addresses. There are 13 root DNS servers at the heart of the DNS system.

•Exploit

A published sample bit of code or program that demonstrates a flaw in software or hardware.

•Firewall

Designed to prevent unauthorized individuals from breaking into a network. Can be employed in both software and hardware.

•Hacker

Within the hacking community, hackers define themselves as computer enthusiasts. They may obtain unauthorized access to computer and network systems but do not have malevolent purposes. (See "cracker.")

•Honeypot

A trap set to lure spammers or hackers to an open machine so the administrator can learn its system's vulnerabilities.

•Internet

A decentralized worldwide network of computers that can communicate with each other using the TCP/IP protocols.

A piece of computer code that is programmed to infect a computer system.

•Node

A computer connected to the Internet.

•Patch

A fix for a software vulnerability or shortcoming.

•Pings

A program sent to determine whether a particular IP address is available. In a malicious attack, a user can program a computer or various zombie computers to send thousands of pings to overwhelm a system.

•Red team

Usually hired by a company or institution to play an adversarial role and hack into computer systems to assess information security.

•Rooted

A machine that's been hacked and can be completely controlled by the hacker.

•Router

Acts as an intermediary between networks.

•SCADA

Stands for Supervisory Control and Data Acquisition. SCADA systems are software used to control hardware, and to gather and analyze data in many industrial systems.